The present invention relates to a bearing case for supporting a bearing of a crankshaft in an engine.
General-purpose engines of an overhead valve (OHV) type or an overhead camshaft (OHC) type are widely used as power sources for lawn mowers, power-driven sprayers, generators, and others. The crankshaft of such engines is generally supported by ball bearings (hereinafter referred to simply as xe2x80x9cbearingxe2x80x9d). In most cases, the crankshaft is supported at both ends thereof by the bearings.
The bearings are held in a crankcase and/or a main bearing case (hereinafter referred to simply as xe2x80x9cbearing casexe2x80x9d) mounted thereto. Generally, the bearing on one side is accommodated in and held by a bearing holder provided in a wall of the crankcase, while the other bearing is accommodated in and held by the bearing case.
FIG. 7 is a cross-sectional view showing a structure of a conventional bearing case. The conventional bearing case 100 includes a bearing holder 102 protruded at the center of a side wall 101 as shown in FIG. 7. Along an outer periphery of the bearing case 100 is formed a crankcase mounting section 103 (hereinafter referred to simply as xe2x80x9cmounting sectionxe2x80x9d) which is to be joined to a cover mounting surface of the crankcase through a gasket. A hollow 104 is formed between the mounting section 103 and the bearing holder 102. The bearing holder 102 accommodates a ball bearing (not shown) therein and thereby supports one end of the crankshaft.
Apart from a force in an axial direction, the crankshaft is subjected to a force exerted orthogonally thereto in an explosion stroke. The bearing accordingly receives the force exerted thereto in a radial direction orthogonal to the crankshaft in addition to the force in the rotational direction. The bearing case 100 shown in FIG. 7 receives such force in the bearing holder 102.
The bearing case 100, however, has a mounting section 103 overhung from the bearing holder 102, and therefore when subjected to a radially acting force, the bearing holder 102 warps from its base end, resulting in deformation in the side wall 101. The radially exerted force also acts on the mounting section 103 as moment, whereupon a compressive force and a shearing force act between the mounting section 103 and the crankcase. The gasket interposed therebetween is subjected to such forces repeatedly and is accordingly deformed over and over again. Thus deterioration of the gasket proceeds quickly, leading to the risk of oil leakage.
In the high-performance engines with higher speed for higher output in recent years, the bearing holder 102 is subjected to ever increasing load. The bearing case shown in FIG. 7 is hardly capable of withstanding such load, and therefore an improvement in the structure of bearing case has been desired.
An object of the present invention is to provide a rigid and light bearing case.
In order to achieve the object, there is provided a bearing case for an engine according to the present invention, which is attached to a crankcase of the engine for supporting the bearing of a crankshaft in the engine, and includes a bearing holder for holding the bearing, a crankcase mounting section formed on an outer peripheral surface of the bearing case to be joined to the crankcase, and a rib wall formed in the bearing case on a side of the crankcase and extending between the bearing holder and the crankcase mounting section.
According to the present invention, a force acting on the bearing holder in a radial direction through the crankshaft is received by the rib wall, so that the bearing holder can be prevented from warping at its base end as the conventional bearing case. Also, the crankcase mounting section receives less moment, whereby its movement is restricted. As a result, damage to the gasket caused by deformation or play of the bearing case is prevented, whereby the lifetime and reliability of the product are improved.
The rib wall may be formed in a spherical shape so as to better support the bearing holder by arched wall surface, thereby enhancing the rigidity of the bearing case. The thickness of the rib wall can be reduced accordingly so as to make the bearing case more lightweight. Vibration and operation noise can also be absorbed and restricted more efficiently by the spherical wall, resulting in overall enhancement of the product performance.
The rib wall is preferably formed on an upper side of the bearing case with respect to the axis of the crankshaft. The lower side of the bearing case is less affected by the radially acting force, and so the rib wall therefor is omitted, thereby increasing a degree of freedom of design with respect to the lower side, from the axis of the crankshaft, of the bearing case.
Additionally, a cavity may be formed on the lower side of the bearing case with respect to the axis of the crankshaft, so as to open toward the side of the crankcase and to form part of an oil pan for the engine. Thereby, the rigidity of the bearing case is improved while the oil reservoir capacity is secured.
The bearing case may further include a reinforcing rib formed along the outer periphery thereof on one surface of the crankcase mounting section on the opposite side from the crankcase, for securing rigidity of the bearing case in its surface direction.
Preferably, the crankcase mounting section includes a plurality of bolt holes for passing a plurality of bolts therethrough so as to fixedly couple the bearing case to the crankcase, the reinforcing rib being formed so as to connect these bolt holes. The reinforcing rib is preferably formed to part of the bearing case where the above-mentioned rib wall exists.